Preparation and characterization of nickel hybrid material and its catalytic activity

Abstract

An organic-inorganic hybrid metal phosphate was synthetized by hydrothermal route at 180 °C. It was characterized by X-ray diffraction (XRD), thermal and chemical analysis, FTIR and NMR spectroscopies, Electron Spin Resonance (ESR), SEM analysis and UV–Visible diffuse reflectance. These analyses allowed us to propose the formula Na[PW₆Ni₃O₂₇][C₂N₂H₁₀]_0.5[C₂N₂H₉]₃·3H₂O (Ni-Ethylene Diamine) and thermal gravimetry shows stability up to 350 °C. Increasing conductivity with temperature indicates a semiconducting behavior with a room temperature conductivity σ_{300 K} of 1.2 × 10^–4 (Ω-cm)^-1. The paramagnetic ion Ni(II) (3d⁷), produces a disturbance in the NMR spectra. The FT-IR spectrum shows peaks at 500 and 730 cm^-1, attributed respectively to Ni-O and W-O bonds while the characteristic peak of PO₄ is observed at 1030 cm^-1. SEM micrograph shows crystals in the form of hexagonal needles with more or less homogeneous shapes (∼ 15 µm) and an average porosity. The UV–Visible spectrum of the hybrid compound shows two bands at 250 and 320 nm, attributed to ligand-metal charge transfer (O^2-: 2p → Ni²⁺: 4 s). The indirect allowed transition (2.30 eV) is assigned to the internal transition of Ni²⁺ (e → t₂). The ESR spectrum indicates a g-factor of 2.005, a signature of Ni²⁺ tetrahedrally bonded to O₂^- ions. The compound was successfully tested in the oxidation of acetaldehyde (CH₃CHO) to acetic acid (CH₃COOH). This study was conducted by varying two parameters namely the temperature (40, 50 and 60 °C) and the nature of the oxidant: H₂O₂ and tert‑butyl hydroxide peroxide. The best result is obtained with H₂O₂ at 60 °C, with an activity twice as high as without catalyst.